High performance sprag clutch assembly

ABSTRACT

A high performance sprag clutch assembly and replacement system for a land motor vehicle transmission, which utilizes a commercially available sprag assembly popular among high performance enthusiasts in combination with newly manufactured inner and outer races to achieve the maximum rated torque capacity is disclosed. The outer race and stator end cap components have been designed to reduce the overall axial length to adapt the sprag clutch assembly to the limited axial space within the stator component of the torque converter of various transmissions. The interlocking stator caps function to reduce race eccentricity under load to ensure that each individual sprag element carries the torque equally to prevent the sprag elements from being rolled over in operation causing severe damage. A plurality of interchangeable inner races adapt the present sprag clutch system for use with GENERAL MOTORS, FORD, and CHRYSLER transmission input shaft configurations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. 119(e) of U.S.Provisional Patent Application No. 60/365,911 filed Mar. 21, 2002,entitled Improved Sprag Clutch Assembly.

BACKGROUND OF THE INVENTION

The present invention relates to the field of one-way clutches for usein land motor vehicles and, more particularly, to a high performancesprag clutch assembly for use in the torque converter stator of anautomatic transmission.

The original concept of the sprag clutch was developed in the late1940s. Since that time sprag clutches have been used as driving membersin many automatic transmissions worldwide. Sprag clutches are a specificclass of one-way clutches. The unique feature of one-way clutches isthat they can maintain high torque capacity in one direction and notorque capacity in the other direction.

The geometric design characterizing sprag clutch operation basicallyinvolves unidirectional wedging of the surfaces of multiple-camstructures denoted as dogleg sprags or sprag elements between two races,which enclose the sprags. The primary role of the sprag clutch in thepresent application is to allow the stator component within a torqueconverter in an automatic transmission to be driven by the torqueconverter in only one direction. This occurs at high load conditionsduring which the sprag elements are wedged in the drive mode to preventrelative motion between the inner and outer races. In this mode andduring the transition to engagement, the wedged sprags transmit torquefrom the outer race to the inner race of the clutch.

Reliable sprag clutch operation requires a number of contributing designfactors. (1) The clutch design must force all of the sprags to worktogether in phase throughout their operating range (so-called “phasing”)such that the sprags equally share the load within small tolerancevariations. (2) All sprags should be individually energized, axiallyaligned, and as free as possible of parasitic friction that subtractsfrom the normal energizing forces. (3) Adequate race proportions,concentricity, material, heat treatment, and surface finish areessential. Thus, the clutch is no better than the races used in itsfabrication. (4) The clutch must be adequately lubricated. Lubricationrequirements will vary significantly depending on application details.

The typical problem in sprag clutch design is to achieve the greatestpossible torque capacity in a minimum of space. Maximum and minimumsprag lengths are usually governed by practical considerations. Forexample, the maximum length is limited by the ability to heat-treatwithout distortion; and the minimum length is governed by the divisionof the axial space available between sprag and the energizing means(i.e. cages).

There are several known prior art patents that are available in thefield and their discussion follows. One example of a prior art one-wayclutch is disclosed in U.S. Pat. No. 5,779,014 to Kinoshita et al.,which teaches a one-way clutch mounting structure including an outerring, an inner ring and a plurality of clutch members interposed betweenthe inner and outer rings. In this one-way clutch the outer ring ismounted in a housing, which is part of a stator. The housing has anannular section and a side section, which together define a pocketwherein the outer ring is mounted. The outer ring includes a spiralengaging means providing an integrated structure between the statorhousing and the outer ring.

Another example of a prior art one-way clutch for a torque converter isdisclosed in U.S. Pat. No. 5,760,514 to Taniguchi et al., which providesa one-way clutch for a plastic stator capable of preventing the innercircumferential surface of the outer ring of the one-way clutch frombeing deformed during shrinkage of the plastic stator in themanufacturing process. Thus, the outer ring integrally formed with theplastic stator is not required to be further machined after theintegration, which reduces production costs.

U.S. Pat. No. 6,481,549 to Kroll et al. discloses an overrunning clutchfor a torque converter wherein the stator consists of glass reinforcedplastic which is injected around the overrunning clutch outer ring sothat machining of the outer ring is no longer necessary afterintegration in the stator.

U.S. Pat. No. 5,881,556 to Matsuoka discloses a stator for a torqueconverter with thrust supporting structures without using a thrustbearing on at least one axial end thereby facilitating reduction of theaxial dimensions thereof.

While these devices fulfill their respective, particular objectives andrequirements, the aforementioned patents do not disclose the highperformance sprag clutch assembly of the present invention, whichsubstantially departs from the conventional concepts and designs of theprior art.

SUMMARY OF THE INVENTION

Accordingly, the present invention is a high performance sprag clutchassembly, which utilizes a standard, commercially available spragassembly in combination with the newly manufactured inner and outerraces of the present invention to achieve the maximum rated torquecapacity and to minimize manufacturing costs. The present outer race andstator cap components have been designed to reduce the overall axiallength of the sprag clutch assembly in order to adapt a BORG WARNER(Part No. 27306 AM) sprag assembly, which is popular among racingenthusiasts, to the limited axial space within the stator component ofthe torque converter. Interlocking stator caps function to reduceeccentric loading of the races in operation to ensure that eachindividual sprag element carries the torque equally and to prevent thesprag elements from being rolled over in operation. A plurality ofinterchangeable inner races having different internal splineconfigurations adapt the present sprag clutch assembly for use withvarious transmission shafts including twenty-seven-tooth spline shafts,thirty-two-tooth stator support shafts, and various other shaft splineconfigurations utilized in GENERAL MOTORS, FORD, and CHRYSLERtransmissions.

There has thus been outlined, rather broadly, the important features ofthe present invention in order that the detailed description thereofthat follows may be better understood, and in order that the presentcontribution to the art may be better appreciated.

Other features and technical advantages of the present invention willbecome apparent from a study of the following description and theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the present invention are set forth in theappended claims. The invention itself, however, as well as otherfeatures and advantages thereof will be best understood by reference tothe following detailed description of an illustrative embodiment whenread in conjunction with the accompanying figures, wherein:

FIG. 1 is a composite view illustrating the components of a typicalsprag clutch labeled Prior Art;

FIG. 2 is a composite diagram illustrating the sprag clutch in the drivemode (clutch engaged) and the freewheeling mode (clutch disengaged);

FIGS. 3A–3C show partial sections of the sprag clutch illustrating thephasing of the sprags throughout the entire operating range;

FIG. 4 is an elevational view of the improved sprag clutch assembly ofthe present invention;

FIG. 5A is an elevational view of the inner race of the present spragclutch;

FIG. 5B is a cross-sectional view of the inner race taken along thesection line 5B—5B of FIG. 5A;

FIG. 6A is an elevational view of the outer race of the present spragclutch;

FIG. 6B is a cross-sectional view of the outer race taken through thesection line 6B—6B of FIG. 6A;

FIG. 7A is an exploded cross-sectional view of the present sprag clutchshowing the details of the stator cap components; and

FIG. 7B is a cross-sectional view showing the components of the presentsprag clutch in an assembled condition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Prior to describing the present invention in detail it may be beneficialto briefly review the structure and function of a typical sprag clutchin an automatic transmission. With reference to the drawings there isshown therein a sprag clutch in accordance with the prior art, indicatedgenerally at 100 and illustrated in FIG. 1.

The primary components of the sprag clutch 100 consist of the spragassembly, indicated generally at 110, an inner race 112, an outer race115, two end bearings 116, and two retaining rings 118 (only one shown).The sprag assembly 110 typically consists of a plurality of spragelements or sprags 105 held in place by two concentric cages 107, 108positioned between the inner and outer races 112, 115 as most clearlyshown in FIG. 2. A stamped, spring-steel ribbon 109 located between thecages 107, 108 pre-loads the sprags 105 evenly to distribute the loadduring engagement. This is accomplished by spring tabs (not shown) thatare formed on the spring ribbon 109 each of which is in contact with asprag 105. The end bearings 116 and the retaining rings 118 align thesprag assembly 110 axially between the inner and outer races 112, 115.

In most sprag clutch applications the inner race 112 overruns the outerrace 115 in the same direction at about twice the outer race speed.Since no load is applied to the sprag assembly 100 in this state, thiscondition is regarded as freewheeling (FIG. 2 at the right). The ribbon109 keeps each element in constant contact with the inner race 112 sothat engagement and torque transfer, when required, can be both rapidand coincident for all the sprag elements 105. This occurs when thesprag elements 105 are wedged (i.e. locked) in the drive mode to preventrelative motion between the inner and outer races 112, 115 as shown(FIG. 2 at the left). In this mode and during the transition toengagement, the wedged sprag elements 105 transmit torque directly fromthe outer race 17 to the inner race 15.

Phasing of the sprag elements 105 is achieved by the use of the twocages 107, 108 that are held concentric by their respective races 112,115. The outer cage 108 controls the sprags 105 near their outer racecontact and the inner cage 107 controls the sprags 105 near the innerrace contact. By accurately sizing and spacing the cage openings whereinthey are disposed, the sprags 105 can be contoured and fitted so theymove in unison throughout their entire operating range. FIGS. 3A–3C showthe relationship of sprags 105 and cages 107, 108 during the driven mode(FIG. 3A), transition mode (FIG. 3B), and freewheeling mode (FIG. 3C).

Thus, it will be appreciated that multiple forces act upon the spragelements 105. In the drive mode the inner race 112 experiences thewedging force transmitted by the sprag assembly 105 from the outer race115. In the freewheeling mode the centrifugal force acting on the spragassembly 100 during high differential speeds tends to load the spragelements 105 against the inner race 112, which contributes largely tothe total drag force. An additional secondary force is produced by thespring tabs (not shown) acting on the sprag elements 105, whichgenerates frictional drag on the inner race 112.

An assumption made by most manufacturers is that the clutch races 1112,115 are precisely concentric when the sprag elements 105 first engageand begin to transmit torque. Unfortunately, this condition is noteasily achieved in actual practice. Depending on the clutch, spragelement angle, and spring design, the races 112, 115 are forced into aneccentric condition and a substantial percentage of the sprag elements105 never carry any of the torque. The few remaining load-bearing spragelements 105 in such condition can be overloaded and rolled over causingclutch failure. The effect of the eccentric push on bearings associatedwith the races 112, 115 is sometimes damaging to the bearings.

One reason for the eccentric loading is that the loaded sprags 105 inthe larger radial sprag space between the races have a greater cam riseper degree of rotation than the loaded sprags 105 in the smaller radialsprag space caused by the eccentricity. Thus, as the torque is increasedthe races 112, 115 are held eccentric or are forced into a position ofgreater eccentricity depending on the extent of the original offset.

The present invention has been developed to minimize these problems andwill now be described in detail. With reference to FIG. 4 there is showntherein an improved sprag clutch in accordance with the presentinvention, indicated generally at 10. The sprag clutch 10 is comprisedof an inner race 15, an outer race 17, a sprag assembly 110 and a pairof opposed stator caps 25 (FIG. 7A). A sprag assembly 110 manufacturedunder the tradename BORG WARNER (Part No. 27306 AM) or another similarsprag assembly is desirable for this purpose.

The primary role of the present sprag clutch assembly 10 is to allow therotating, shaft-mounted stator wherein it is installed to be driven inonly one direction. In the present application the inner race 15 isalways stationary. The sprag clutch 10 engages (i.e. locks up) when thetorque converter is loaded. When the load decreases and parasitic dragon the stator increases, the stator, which is connected to the outerrace 17 freewheels.

In a typical embodiment the inner race 15 is a cylindrical constructionincluding an internal spline 12 formed in the inside diameter as shownin FIGS. 5A and 5B. In the embodiment shown the internal spline 12consists of twenty-seven teeth 14 for mating engagement with a 27 toothspline pattern on the transmission input shaft 16 (shaft is shownwithdrawn for clarification). In accordance with the present inventionthe inner race 15 is provided in other spline configurations so as to beinterchangeable for different applications. For example, the inner race15 is provided in alternative embodiments (not shown) adaptable to a 32tooth stator support shafts utilized in FORD transmissions and variousother spline patterns.

Referring to FIGS. 6A and 6B the details of the present outer race 17are illustrated. The outer race 17 includes a plurality of slots 18formed on the circumference, which engage mating key structures (notshown) formed on the inside diameter (I.D.) of the stator component toprovide positive engagement and to ensure rotation of the stator duringoperation. As shown in cross-section in FIG. 6B, the outside diameter(O.D.) of the outer race 17 as at 40 is machined in a steppedconfiguration to provide interlocking engagement with the stator endcaps 25 (FIGS. 7A and 7B).

The stator end caps, indicated generally at 25, are designed to securethe inner and outer races 15, 17 in coaxial alignment with the spragassembly 110. Thus, it will be appreciated that the stator end caps 25provide essentially the same function as the end bearings 116 andretaining rings 118 of the prior art sprag clutch 100. A plurality ofoil slots 32 extending inwardly as most clearly shown in FIG. 4 providescontinuous lubrication to the sprag assembly 110 and inner race 15.

The counterbores 30, 35 wherein the inner and outer races 15, 17 engagethe stator end caps 25 are machined to hold precise concentricitytolerances to ensure that, when the sprag clutch 10 is assembled asshown in FIG. 7B, the races 15, 17 are maintained in concentricrelation. Thus, potential for eccentric loading of the inner and outerraces 15, 17 and the rollover of sprags 105 is minimized.

Further, when the present sprag clutch 10 is assembled such that theinner and outer races 15, 17 are interlocked within the counterbores 30,35 in the stator end caps 25, the overall axial length as at “X” (FIG.7B) is reduced to a minimum to meet the space restrictions for thisapplication.

Although not specifically illustrated in the drawings, it should beunderstood that additional equipment and structural components will beprovided as necessary and that all of the components described above arearranged and supported in an appropriate fashion to form a complete,operative, and Sprag Clutch Assembly incorporating features of thepresent invention. For example, it is anticipated that the present spragclutch assembly may be provided in a kit form including at least oneinterchangeable inner race for various torque converter statorapplications. In addition, the present sprag clutch assembly may beincluded within a complete torque converter rebuild kit having othertorque converter components.

Moreover, although illustrative embodiments of the invention have beendescribed, a latitude of modification, change, and substitution isintended in the foregoing disclosure, and in certain instances somefeatures of the invention will be employed without a corresponding useof other features. Accordingly, it is appropriate that the appendedclaims be construed broadly and in a manner consistent with the scope ofinvention.

1. A sprag clutch assembly for a land motor vehicle transmission, saidsprag clutch assembly comprising: at least one interchangeable innerrace including an internal spline having a predetermined number ofspline teeth formed therein; a cylindrical outer race radially disposedabout said inner race; a sprag assembly including a plurality of spragelements, wherein said sprag assembly is disposed intermediate saidinner race and said outer race; and a pair of stator end caps disposedin interlocking engagement with said inner race and said outer race suchthat said races are held in concentric relation to supportunidirectional wedging of said sprag elements between said inner andsaid outer races said inner race and said outer race being capturedwithin mating concentric counterbores formed in each of said pair ofstator end caps, said counterbores being machined to a preciseconcentricity tolerance to minimize eccentric loading of said inner raceand said outer race during operation.
 2. The sprag clutch assembly ofclaim 1 wherein said sprag assembly is a commercially available BORGWARNER sprag assembly comprised of twenty-two sprag elements.
 3. Thesprag clutch assembly of claim 1 wherein said interchangeable inner raceincludes an internal spline formed therein configured for engagementwith a mating external spline formed on a transmission input shaft. 4.The sprag clutch assembly of claim 3 wherein said internal splinecomprises twenty-seven spline teeth.
 5. The sprag clutch assembly ofclaim 3 wherein said internal spline comprises thirty-two spline teeth.6. An improved sprag clutch assembly for a torque converter stator in aland vehicle transmission, wherein the sprag clutch assembly includes aplurality of sprag elements disposed intermediate an inner race and anouter race providing high torque capacity in one direction and no torquecapacity in the other direction, wherein the improvement comprises: aplurality of interchangeable inner races, wherein each of said innerraces includes an internal spline having a different number of teethformed therein; a cylindrical outer race radially disposed about saidinner race, wherein said outer race has a stepped cross-sectionalprofile having a plurality of outside diameter dimensions; and a pair ofstator end caps disposed in interlocking engagement with said inner raceand said outer race to support in-phase wedging of the sprag elementsbetween the inner and the outer races.
 7. The improved sprag clutchassembly of claim 6 wherein said sprag assembly is a commerciallyavailable BORG WARNER sprag assembly comprised of twenty-two spragelements.
 8. The improved sprag clutch assembly of claim 6 wherein saidinner race and said outer race are captured within a pair of matingconcentric counterbores formed in each of said pair of stator end caps,wherein said counterbores are machined to a precise concentricitytolerance to minimize eccentric loading of said inner race and saidouter race during operation.
 9. The improved sprag clutch assembly ofclaim 7 wherein at least one of said plurality of interchangeable innerraces includes an internal spline configured for engagement with amating external spline formed on a transmission input shaft.
 10. Theimproved sprag clutch assembly of claim 9 wherein said mating internalspline comprises twenty-seven spline teeth.
 11. The improved spragclutch assembly of claim 9 wherein said mating internal spline comprisesthirty-two spline teeth.
 12. A method of adapting a preexisting spragassembly for use in a unidirectional sprag clutch installed in thetorque converter stator of a land motor vehicle transmission, saidmethod comprising the steps of: fabricating a plurality ofinterchangeable inner races each including an internal spline having adifferent number of teeth formed therein for mating engagement with asplined input shaft of a transmission; furnishing at least onecylindrical outer race for radial placement about said plurality ofinterchangeable inner races; installing a sprag assembly having aplurality of sprag elements intermediate said inner race and said outerrace; and interlocking a pair of stator end caps in engagement with saidinner race and said outer race such that said races are captured inprecise concentric relation to support in-phase wedging of said spragelements between said inner and said outer races resulting in hightorque capacity in one direction and no torque capacity in the oppositedirection.
 13. The method of claim 12 wherein the step of interlockingfurther includes the steps of: machining at least two concentriccounterbores in each stator end cap corresponding to the dimensions ofsaid inner race and said outer race, wherein said inner race and saidouter race are engaged within said counterbores; and minimizing theoverall axial length of the sprag clutch assembly to conform to alimited axial space within the torque converter stator.
 14. A spragclutch replacement system for installing a preexisting sprag assembly inthe torque converter stator of a land vehicle transmission, saidreplacement system comprising: a plurality of interchangeable innerraces, wherein each of said inner races includes an internal splinehaving a different number of teeth; a cylindrical outer race radiallydisposed about one of said plurality of interchangeable inner races; asprag assembly including a plurality of sprag elements disposedintermediate said inner race and said outer race; and a pair of statorend caps disposed in interlocking engagement with said inner race andsaid outer race such that said races are held in concentric relation toallow unidirectional wedging of said sprag elements between said innerand said outer races providing high torque capacity in one direction andno torque capacity in the opposite direction.
 15. The sprag clutchassembly of claim 14 wherein said sprag assembly is comprised oftwenty-two sprag elements.
 16. The sprag clutch assembly of claim 14wherein said inner race and said outer race are captured within a pairof mating counterbores formed in each of said pair of stator end caps,wherein said counterbores are machined to a precise concentricitytolerance to minimize eccentric loading of said inner race and saidouter race during operation.
 17. The sprag clutch assembly of claim 14wherein said cylindrical outer race has a stepped cross-sectionalconfiguration having a plurality of outside diameter dimensions, saidstepped cross-sectional configuration providing a reduced axial lengthof said sprag clutch assembly upon interlocking engagement of said outerrace with said pair of stator end caps.